Hi tinku:
The software WinRAR will serve you for opening as well as compressing files.
For this software, I do not know if the ratio of compression can be chosen in advance. My experience is that it depends on the type of file that is going to be compressed. For example, MSWord files can be reduced in size by a big margin.
You may find useful information in the website[link Point to another website Only the registered members can access]
Regards





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